This invention relates to a method for preparing a magnetic recording medium and to a physical vapor deposition device.
In recent years, higher densification of magnetic recording medium such as tape, disc, etc. has been strongly demanded, and researches and developments of various methods for preparation of medium are under progress. A method in which a metal thin film is used for the magnetic recording layer of a magnetic recording medium is one of them.
As the method for forming the metal thin film recording layer, the wet process method by plating and the physical vapor deposition method such as vacuum vapor deposition, sputtering, etc. have been studied. In the wet process method, management of the plating bath is cumbersome and therefore it is not suitable for continuous film formation and also severe management is required in disposal of waste liquors, thus involving many problems. Therefore, the use of physical vapor deposition processes for film formation has become accepted in the art.
As the magnetic recording layer, a vertically magnetized film capable of accomplishing high density recording has recently been widely studied. As the vertical magnetized film, a Co type alloy is effective.
In the case of forming a magnetic recording layer of vertically magnetized film, for obtaining desired magnetic characteristics, it is required in most cases to form a film of the magnetic recording layer while heating the non-magnetic substrate. However, when a magnetic layer is formed while heating the non-magnetic substrate, wrinkle will be generated on the substrate.
As the method for preparing a magnetic recording layer on a non-magnetic substrate according to the vacuum vapor deposition method or the sputtering method, it is most generally practiced to effect film formation while permitting a polymer substrate to run along a rotary drum. Whereas, when film formation is effected at a high circumferential temperature of the rotary drum, wrinkle will be generated when the polymer substrate contacts the rotary drum. The cause for generation of wrinkle may be considered as follows. When the substrate contacts the rotary drum, the substrate will be abruptly heated because of high temperature of the rotary drum, whereby gas liberation from the substrate and thermal deformation occur. When a gas is generated from the substrate in contact on the rotary drum, gaps are formed between the substrate and the drum, which may become the cause for wrinkle. At the same time, thermal deformation of the substrate is conveyed as such to become wrinkle.
Generation of such wrinkle will occur readily when the circumferential temperature of the rotary drum is 80.degree. C. or higher and become more marked as the thickness of the polymer substrate is smaller, particularly 10 .mu.m or less.
In the prior art, for prevention of generation of wrinkle, there have used the method in which a nip roller 9 is provided as shown in FIG. 5 or the method in which the substrate is heated with a lamp 11 on a pre-heating roller 10. However, these methods proved to be insufficient by the investigation by the present inventors.
The nip roller 9 is intended to prevent generation of wrinkle by pressing the substrate 1, but when the temperature of the rotary drum 2 is high, generation of wrinkle cannot be prevented by pressing of the substrate 1 and the wrinkle is pressed under the nip roller 9 to become folded wrinkle.
In the case of the pre-heating roller 10, when the temperature of the rotary drum 2 becomes higher, the temperature of the pre-heating roller 10 must be also made higher, consequently resulting in formation of wrinkle on the pre-heating roller 10.